1. Field of the Invention
It is generally related to the field of flat display or visual screen having matrix addressing of any size, and can be applied in any industrial sectors using screens of this type: television, computer, telecommunications, monitoring devices, surveillance equipment.
2. Description of the Prior Art
Known microtip screens are vacuum tubes generally constituted of two, imperviously sealed, thin glass plates, the rear plate or cathode plate comprising a matrix network of field effect emitters consisting of microtips, and the front plate or anode plate being covered by a transparent conducting layer and luminophores.
Each luminous point (pixel), is associated with an oppositely located cathodic emitting surface and constituted of a large number of microtips (approximately 10,000 per mm2). This emitting surface is defined by the intersection of a line (grid) and a column (cathodic conductor) of the matrix.
By virtue of the short tip-grid distance (.ltoreq.1 .mu.m) and the amplifying effect of the tip, a potential difference of less than 100 volts applied between line and column enables the obtention, at the top of the tip, of an electric field that is sufficient to cause the emission of electrons and high luminance with a low voltage luminophore.
The conventional structure of the cathode of a microtip screen especially comprises, deposited successively on a substrate of glass or silicon:
an insulation layer; PA1 a resistive layer of silicon or other material; PA1 "column conductors" constituted of a metallic layer which can be deposited either beneath or above the resistive layer; PA1 an insulating layer (Si or SiO2) which constitutes the grid insulator; PA1 a metallic layer which constitutes the grid or line conductors.
After depositing the aforementioned layers, holes in which the microtips are then produced, are drilled into the insulating grid by means of known etching techniques.
The main object of the resistive layer is to limit the current in each emitter in order to homogenize the electronic emission, and to limit the maximum current which would pass through the tip in case of a tip-grid short-circuit.
The load characteristic which results from serializing a resistance with the tip, is a straight line. The voltage drop in this resistance is proportionate to the current which passes through it and can be quite substantial if the current emitted by the dot is substantial. The voltage which must be applied to the protective tip-resistance system is increased proportionately, which substantially affects the screen consumption, in particular.
The object of the present invention is a flat screen having individually dipole-protected microtips.